Introduction
Lipoprotein-associated Phospholipase A2 (Lp-PLA2) is an enzymatically active 50 kD protein that has been associated with Coronary vascular disease (CVD) including coronary heart disease (CHD) and stroke. Lp-PLA2 has been previously identified and characterized in the literature by Tew et al. (1996) Arterioscler. Thromb. Vasc. Biol. 16:591-599, Tjoelker, et al. (1995) Nature 374(6522):549-53), and Caslake et al. (2000) Atherosclerosis 150(2): 413-9. In addition, the protein, assays and methods of use have been described in the patent literature WO 95/00649-A1: U.S. Pat. Nos. 5,981,252, 5,968,818, 6,177,257, 7,052,862, 7,045,329, 7,217,535, 7,416,853; WO 00/24910-A1: U.S. Pat. Nos. 5,532,152; 5,605,801; 5,641,669; 5,656,431; 5,698,403; 5,977,308; and 5,847,088; WO 04/089184; WO 05/001416: U.S. Pat. No. 7,531,316; WO 05/074604; WO 05/113797; the contents of which are hereby incorporated by reference in their entirety. Lp-PLA2 is expressed by macrophages, with increased expression in atherosclerotic lesions (Hakkinin (1999) Arterioscler Thromb Vasc Biol 19(12): 2909-17). Lp-PLA2 circulates in the blood bound mainly to LDL, co-purifies with LDL, and is responsible for >95% of the phospholipase activity associated with LDL (Caslake 2000).
The United States Food and Drug Administration (FDA) has granted clearance for the PLAC® Test (diaDexus, South San Francisco, Calif.) for the quantitative determination of Lp-PLA2 in human plasma or serum, to be used in conjunction with clinical evaluation and patient risk assessment as an aid in predicting risk for coronary heart disease, and ischemic stroke associated with atherosclerosis.
Various methods for detecting Lp-PLA2 protein have been reported which include immunoassays (Caslake, 2000), activity assays (PAF Acetylhydrolase Assay Kit, Cat#760901 product brochure, Cayman Chemical, Ann Arbor, Mich., 12/18/97 (caymanchem with the extension .com of the world wide web); Azwell/Alfresa Auto PAF-AH kit available from the Nesco Company, Alfresa, 2-24-3 Sho, Ibaraki, Osaka, Japan or Karlan Chemicals, Cottonwood, Ariz., see also Kosaka (2000)), spectrophotometric assays for serum platelet activating factor acetylhydrolase activity (Clin Chem Acta 296: 151-161, WO 00/32808 (to Azwell)). Other published methods to detect Lp-PLA2 include WO 00/032808, WO 03/048172, WO 2005/001416, WO 05/074604, WO 05/113797, U.S. Pat. Nos. 5,981,252 and 5,880,273 and U.S. publication No. US 2012-0276569 A1. The contents of the published applications are hereby incorporated by reference in their entirety.
Coronary Heart Disease
Lipoprotein-associated phospholipase A2 (Lp-PLA2) levels have been shown to be significantly correlated in men with angiographically-proven Coronary Heart Disease (CHD) (Caslake 2000) and associated with cardiac events in men with hypercholesterolemia (Packard (2000) N Engl J Med 343(16): 1148-55).
Coronary heart disease (CHD) is the single most prevalent fatal disease in the United States. In the year 2003, an estimated 1.1 million Americans are predicted to have a new or recurrent coronary attack (see the American Heart Association web site, americanheart with the extension .org of the world wide web). Approximately 60% of these individuals have no previously known risk factors. It is apparent that there is a great need to diagnose individuals at risk of developing CHD, selecting patients suitable for therapy and monitoring response to therapies directed at reducing the individual's risk.
Coronary vascular disease (CVD) encompasses all diseases of the vasculature, including high blood pressure, coronary heart disease (CHD), stroke, congenital cardiovascular defects and congestive heart failure. Studies have shown that CHD is responsible for the majority of the CVD. The prevalence of CHD increases markedly as a function of age, with men having a higher prevalence than women within most age groups.
The current standard of care used to identify individuals at risk for heart disease is the measurement of a lipid panel, including triglycerides, total cholesterol, low density lipoprotein (LDL)-cholesterol, and high density lipoprotein (HDL)-cholesterol (Adult Treatment Panel III). Executive Summary of The Third Report of The National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, And Treatment of High Blood Cholesterol In Adults (Adult Treatment Panel III). JAMA (2001) 285(19): 2486-97. According to the recent Adult Treatment Panel III (ATP III) guidelines (2001), depending on the risk factor score, individuals with LDL-cholesterol levels from ≧100 to ≦130 mg/dL are recommended to initiate therapeutic lifestyle changes. Adults with LDL-cholesterol >130 mg/dL are recommended for intensive lifestyle therapy and an LDL-cholesterol-lowering drug therapy to achieve an LDL-cholesterol goal of <100 mg/dL. Patients with LDL levels >160 mg/dL should be considered for therapies with lipid-lowering drugs. The American Heart Association has estimated that over 100 million adults in the US exceed the optimal level of total cholesterol. See the website americanheart with the extension .org of the world wide web.
While research continues to link elevated LDL-cholesterol levels with CHD risk, it is well understood that a significant number of individuals with normal LDL-cholesterol levels experience a cardiac event, suggesting that other factors not currently recognized may be involved (Eaton (1998) J Am Board Fam Pract 11(3): 180-6). In the search for new risk factors, significant attention has been focused in recent years on markers of inflammation, as a growing body of basic and clinical research emerges regarding the role of inflammation in atherogenesis (Lusis (2000) Atherosclerosis. Nature 407(6801): 233-41; Lindahl (2000) N Engl J Med 343(16): 1139-47). Some of the inflammatory markers under investigation include cell adhesion molecules, CD-40 ligand, interleukin 6 and C-reactive protein (CRP, measured by the high sensitivity method, or hsCRP). CRP, a non-specific acute phase inflammatory marker, has recently received significant attention as a potential risk indicator for CHD (Ridker (2002) N Engl J Med 347(20): 1557-65; Blake (2002)); J Intern Med 252(4): 283-94). CRP, however, is well known to be responsive to many sources of inflammation, which justifies further investigations to identify more specific markers of arterial involvement.
The pathogenesis of atherosclerosis leading to the formation of unstable plaque has been recognized as one of the major causes of CHD (Lusis 2000). Recently, new understanding of the pathogenesis of atherosclerosis has placed emphasis on the inflammatory process as a key contributor to the formation of unstable plaque. The instability of the atherosclerotic plaque, rather than the degree of stenosis, is considered to be the primary culprit in the majority of myocardial infarctions (MI). This realization has led to the investigation of plaque biology and recognition that markers of inflammation may be useful as predictors of cardiovascular risk. Among the various candidate markers of inflammation, CRP (measured by high sensitivity method, hs-CRP), a non-specific acute phase inflammatory marker, has received the most attention as a predictor of CHD (Ridker 2002).
Stroke
Stroke is a leading cause of death and disability in the world. Worldwide there are 16 million first time strokes annually and 5.7 million stroke deaths. Eighty-seven percent of these deaths occur in low- and middle-income countries. Globally, there are more than 50 million survivors of stroke and transient ischemic attack (TIA). Of these survivors, at least 1 in 5 will have another stroke within 5 years (Strong K (2007) Lancet Neurol. 6:182-187).
In the United States stroke is the third-leading cause of death with about 150,000 per year. Only heart disease and cancer kill more people.
There are approximately 780,000 strokes per year, of which 600,000 are strokes occurring in patients for the first time and 180,000 are recurrent strokes. These attacks leave a large number of survivors with disabilities. Of the approximately 5-6 million stroke survivors in the United States 15%-30% of stroke victims experience permanent disability and 20% require institutional care at 3 months after onset. The total annual cost of stroke was estimated to be $62.7 billion in 2004 in the United States. See Heron (2007) National Vital Statistics Reports. 56(5):1-96 and Rosamond (2008) Circulation. 117:e25-e146. Accordingly, there is a great need to assess an individual's risk for stroke and to provide appropriate care for those who have had a stroke.
Data presented from the Rotterdam Study—Oei et al (European Society of Cardiology in August 2004) and from the ARIC Study—Ballantyne et al. (Scientific Sessions of the American Heart Association (AHA) in November 2004) indicate Lp-PLA2 is an independent risk factor for stroke. In addition, the ARIC stroke study indicated that the measurement of both hsCRP and Lp-PLA2 was particularly useful for stroke risk assessment. After adjusting for traditional cardiovascular risk factors, lipids and hsCRP, elevated levels of Lp-PLA2 were associated with a doubling of risk for ischemic stroke. As in other stroke epidemiological studies, LDL cholesterol (LDL-C) did not differentiate stroke cases from controls in ARIC. Interestingly, statins lower risk of ischemic stroke (and levels of Lp-PLA2), even though LDL-C is not a reliable predictor of stroke (Ballantyne (2005) Arch Intern Med. 165:2479-2484).
Several studies have evaluated Lp-PLA2 and stroke in acute settings. Elkind et al (Arch Intern Med. 2006; 166:2073-2080) evaluated 467 patients with first-ever ischemic stroke who were followed for four years to determine whether levels of hs-CRP and Lp-PLA2 drawn in the setting of acute stroke (84% drawn within 72 hours of stroke) predict risk of stroke recurrence. Levels of Lp-PLA2 and hs-CRP were weakly correlated. After multivariate analysis, patients with the highest Lp-PLA2 levels had double the risk for recurrent stroke and for the combined outcome of stroke, MI, or vascular death. Lp-PLA2 identifies stroke patients who require the most aggressive treatment to prevent a second event. Cucchiara et al (Stroke. 2009 July; 40(7):2332-6) conclude that many patients with TIA have a high-risk mechanism (large vessel stenosis or cardioembolism) or will experience stroke/death within 90 days. The results from their study suggest a potential role for measuring Lp-PLA2 for short-term risk stratification of patients with acute TIA. A review article by Philip Gorelick (Am J Cardiol. 2008; 101[suppl]:34F-40F) provides the first published review of several important prospective epidemiological studies of Lp-PLA2 and risk of stroke. He finds that the “Lp-PLA2 immunoassay may prove to be especially useful for proper risk classification of persons with stroke or cardiovascular diseases who are found to be at moderate risk. It appears useful in overall cardiovascular risk classification and may lead to more aggressive therapeutic approaches with statin agents for lipid control or with other high-risk patient approaches for cardiovascular disease reduction.” Dr. Gorlick characterizes the findings of Furie et al. (Stroke 2007; 38:458) in a study evaluating Lp-PLA2 in patients with acute ischemic stroke stating “Lp-PLA2 was a significant predictor of risk of early stroke recurrence at 6 month and remained significant after multivariate adjustment for diabetes, hypertension, hyperlipidemia, atrial fibrillation, smoking and stroke subtype.”
While Lp-PLA2 has previously been shown to be associated with primary and secondary stroke and useful as a marker to assess risk of stroke, no data have shown Lp-PLA2 as a useful marker to select patients who will benefit from therapy in an acute setting.
Peripheral Vascular Disease and Additional Disease
Peripheral vascular disease (PVD) is a nearly pandemic condition that has the potential to cause loss of limb, or even loss of life. PVD manifests as insufficient tissue perfusion caused by existing atherosclerosis that may be acutely compounded by either emboli or thrombi. Because of the connection between Lp-PLA2, atherosclerosis and vascular inflammation, measurement of Lp-PLA2 levels may be useful for detecting, diagnosing or monitoring PVD. Recently, Santos et al. reported studies of Lp-PLA2 and ankle-brachial index (ABI) a measure of peripheral vascular disease. They found Lp-PLA2 was a borderline-significant predictor of lower ABI (p=0.05) whereas the other markers studied, CRP and white blood count (WBC), were not significant (Santos (2004) Vasc Med. 9(3):171-6).
Lp-PLA2 has been implicated in several other diseases including respiratory distress syndrome (Grissom (2003) Crit Care Med. 31(3):770-5), immunoglobulin A nephropathy (Yoon (2002) Clin Genet. 62(2):128-34), graft patency of femoropopliteal bypass (Unno (2002) Surgery 132(1):66-71), oral-inflammation (McManus and Pinckard (2000) Crit Rev Oral Biol Med. II (2):240-58), airway inflammation and hyperreactivity (Henderson (2000) J. Immunol. 15; 164(6):3360-7), HIV and AIDS (Khovidhunkit (1999) Metabolism 48(12):1524-31), asthma (Satoh (1999) Am J Respir Crit Care Med. 159(3):974-9), juvenile rheumatoid arthritis (Tselepis (1999) Arthritis Rheum. 42(2):373-83), human middle ear effusions (Tsuji (1998) ORL J Otorhinolaryngol Relat Spec. 60(1):25-9), schizophrenia (Bell (1997) Biochem Biophys Res Commun. 29; 241(3):630-59), necrotizing enterocolitis development (Muguruma, (1997) Adv Exp Med Biol. 407:3 79-82), and ischemic bowel necrosis (Furukawa (1993) Pediatr Res. 34(2):237-41).
Molecular Basis for Disease
Oxidation of LDL in the endothelial space of the artery is considered a critical step in the development of atherosclerosis. Oxidized LDL, unlike native LDL, has been shown to be associated with a host of pro-inflammatory and pro-atherogenic activities, which can ultimately lead to atherosclerotic plaque formation (Glass (2001) Cell 104(4): 503-16; Witztum (1994) Lancet 344(8925): 793-5). Increasing evidence from basic research suggests that atherosclerosis has an inflammatory component and represents much more than simple accumulation of lipids in the vessel wall. The earliest manifestation of a lesion is the fatty streak, largely composed of lipid-laden macrophages known as foam cells. The precursors of these cells are circulating monocytes. The ensuing inflammatory response can further stimulate migration and proliferation of smooth muscle cells and monocytes to the site of injury, to form an intermediate lesion. As layers of macrophages and smooth muscle cells accumulate, a fibrous plaque is formed, which is characterized by a necrotic core composed of cellular debris, lipids, cholesterol, calcium salts and a fibrous cap of smooth muscle, collagen and proteoglycans. Gradual growth of this advanced lesion may eventually project into the arterial lumen, impeding the flow of blood. Further progression of atherosclerosis may lead to plaque rupture and subsequent thrombus formation, resulting in acute coronary syndromes such as unstable angina, MI or sudden ischemic death (Davies (2000) Heart 83:361-366; Libby (1996) Curr Opin Lipidol 7(5): 330-5).
Lp-PLA2 plays a key role in the process of atherogenesis by hydrolyzing the sn-2 fatty acid of oxidatively modified LDL, resulting in the formation of lysophosphatidylcholine and oxidized free fatty acids (Macphee (1999) Biochem J 338 (Pt 2): 479-87). Both of these oxidized phospholipid products of Lp-PLA2 action are thought to contribute to the development and progression of atherosclerosis, by their ability to attract monocytes and contribute to foam cell formation, among other pro-inflammatory actions (Macphee (2001) Curr Opin Pharmacol 1(2): 121-5; Macphee (2002) Expert Opin Ther Targets 6(3): 309-14).
Clinical Evidence
Lp-PLA2 has been previously reported as a potential risk factor for CHD. The predictive value of plasma levels of Lp-PLA2 for CHD has been reported in a large, prospective case-control clinical trial involving 6,595 men with hypercholesterolemia, known as the West of Scotland Coronary Prevention Study (WOSCOPS) (Packard 2000). Lp-PLA2 was measured in 580 CHD cases (defined by non-fatal MI, death from CHD, or a revascularization procedure) and 1,160 matched controls. The results indicated that plasma levels of Lp-PLA2 were significantly associated with development of CHD events by univariate and multivariate analyses, with almost a doubling of the relative risk for CHD events for the highest quintile of Lp-PLA2 compared to the lowest quintile. The association of Lp-PLA2 with CHD was independent of traditional risk factors such as LDL-cholesterol and other variables. This study provided an encouraging preliminary indication of the clinical utility of Lp-PLA2 as a risk factor for CHD.
Furthermore, in a study of angiographically proven CHD, Lp-PLA2 was shown to be significantly associated with the extent of coronary stenosis (Caslake 2000).
In another study, in which only females were examined (n=246, 123 cases and 123 controls), baseline levels of Lp-PLA2 were higher among cases than controls (p=0.016), but was not significantly associated with CHD when adjusted for other cardiovascular risk factors. In this study, cases included 40% of women with stroke, 51% non-fatal myocardial infarction and 9% fatal CHD (Blake (2001) J Am Coll Cardiol 38(5): 1302-6).
Recently, several large studies have added to the clinical evidence. For example, the Atherosclerosis Risk in Communities Study (ARIC) was designed to study, over a ten year period, the etiology, risk factors, clinical sequelae, and treatment alternatives for atherosclerosis. It was sponsored by the National Institutes of Health (NIH) and involved 15,792 apparently healthy men and women, aged 45 to 64, in four communities in the United States. In a retrospective study using banked samples, individuals with LDL <130 mg/dL but elevated levels of Lp-PLA2 (highest tertile) had a 2.08-fold higher risk of a coronary event compared to those individuals with low levels of Lp-PLA2 (Ballantyne (2004) Circulation. 109(7):837-42).
Monitoring Trends and Determinants in Cardiovascular Diseases Study (MONICA) was a recent World Health Organization project collecting data from 282,279 apparently healthy men from urban and rural areas in twenty-one countries. In a subsequent study using serum samples from a sub-population of the MONICA subjects, the association between Lp-PLA2 and coronary events was investigated. In this sub-study, 934 men, aged 45 to 64, were followed for 14 years. Mean baseline levels of Lp-PLA2 were significantly higher in the cases versus the non-cases (p=0.01). A one standard deviation increase in Lp-PLA2 concentration as measured by an ELISA was associated in a univariate analysis with a relative risk of 1.37 (p=0.0002), and the risk association remained statistically significant even after adjusting for other factors such as age, diabetes, smoking, blood pressure, lipid levels, BMI and CRP level (relative risk: 1.21; p<0.04). In this study, individuals with the highest levels of both Lp-PLA2 and CRP had a 1.9-fold greater risk than individuals with low levels of both markers.
Lp-PLA2 has been cleared by the FDA for predicting risk for coronary heart disease, and ischemic stroke associated with atherosclerosis. These data support the utility of Lp-PLA2 to predict a first ever stroke and is beginning to be suggested as a marker to predict a second stroke or vascular event after a first cerebrovascular event.
Alberts et al showed at the ISC in New Orleans (Stroke. 2008; 39(2):642) a meta-analysis reviewing five published prospective epidemiological studies confirming the association of elevated Lp-PLA2 and the risk of stroke (Atherosclerosis Risk in Communities (ARIC), 2005, Healthy middle-aged adults; Rotterdam Study, 2005, Healthy men and women; Veterans Affairs HDL Intervention Trial (VA-HIT), 2006, Recurrent CV events, low LDL and low HDL; Women's Health Initiative Observational Study, 2008, Postmenopausal women; Malmo Diet and Cancer Study, 2008, 5393 (60% women) healthy subjects).
In a study evaluating recurrent strokes (Elkind et al, 2006) Lp-PLA2 was related with an increased risk of recurrent stroke (adjusted hazard ratio, 2.08; 95% confidence interval, 1.04-4.18) and of the combined outcome of recurrent stroke, MI, or vascular death (adjusted hazard ratio, 1.86; 95% confidence interval, 1.01-3.42). However in the study by Furie presented at the ISC 2007, an association was found for a recurrent stroke within the next 6 months after a first stroke 1.014 (1.3-6.6), but not for the combined endpoint of stroke, MI or vascular death.
Lp-PLA2 Therapies
Several papers have been published citing the potential of Lp-PLA2 as a therapeutic target for the treatment of coronary artery disease and atherosclerosis (Caslake 2000; Macphee 2001; Carpenter (2001) FEBS Lett. 505(3):357-63; Leach (2001) Farmaco 56 (1-2): 45-50). Evidence that Lp-PLA2 is a therapeutic target for the treatment of CHD has been published in many articles describing several genuses of inhibitors of Lp-PLA2 and their use. These genuses include but are not limited to: azetidinone inhibitors, SB-222657, SB-223777 (MacPhee 1999); reversible 2-(alkylthio)-pyrimidin-4-ones (Boyd et al. (2000) Bioorg Med Chem Lett. 10(4):395-8); natural product derived inhibitors, SB-253514 and analogues (Pinto (2000); Bioorg Med Chem Lett. 10(17):2015-7); inhibitors produced by Pseudomonas fluorescens DSM 11579, SB-253514 and analogues (Thirkettle (2000) et al. J Antibiot (Tokyo). 53(7):664-9; Busby (2000) J Antibiot (Tokyo). 53(7):670-6; Thirkettle (2000) J Antibiot (Tokyo). 53(7):733-5); 2-(alkylthio)-pyrimidones, orally active 1-((amidolinked)-alkyl)-pyrimidones (Boyd et al. (2000) Bioorg Med Chem Lett. 10(22):2557-61); modified pyrimidone 5-substituent in 1-((amidolinked)-alkyl)-pyrimidones is highly water soluble (Boyd, et al. (2001) Bioorg Med Chem Lett. 2001 11(5):701-4); phenylpiperazineacetamide derivative of lipophilic 1-substituent in 1-((amidolinked)-alkyl)-pyrimidones (Bloomer (2001) Bioorg Med Chem Lett. 11(14):1925-9); 5-(Pyrazolylmethyl) derivative and 5-(methoxypyrimidinylmethyl) derivative of 1-(biphenylmethylamidoalkyl)-pyrimidones (Boyd et al. (2002) Bioorg Med Chem Lett. 12(1):51-5); cyclopentyl fused derivative, SB-480848, of the pyrimidone 5-substituent in clinical candidate SB-435495 (Blackie (2003) Bioorg Med Chem Lett. 2003 Mar. 24; 13(6):1067-70). To date, GlaxoSmithKline (GSK) has announced positive clinical data for a novel compound, darapladib, that dramatically lowers Lp-PLA2 activity. Darapladib and other Lp-PLA2 inhibitors, including ralapladib, may represent a new generation of drugs that reduce cardiovascular disease and death.
Winkler recently reported a multicenter, double-blind, randomized study evaluating the effects of fluvastatin XL versus placebo on the level of Lp-PLA2 in 89 patients with type 2 diabetes (42 fluvastatin and 47 placebo) (Winkler (2004) J Clin Endocrinol Metab. 89 (3) 1153-1159). Among these subjects, higher Lp-PLA2 activity was significantly associated with a history of CAD. The highest quartile in terms of Lp-PLA2 activity was at significantly greater risk than the lowest quartile (risk ratio: 2.09; 95% CI: 1.02-4.29; p=0.043). Fluvastatin treatment decreased Lp-PLA2 activity by 22.8%. Blankenberg also reported that taking statins lowered the measurable Lp-PLA2 activity (Blankenberg (2003) J of Lipid Research 44: 1381-1386).
Albert et al reported on the effect of statin therapy on lipoprotein associated phospholipase a2 levels. The researchers evaluated the effect of pravastatin 40 mg daily vs. placebo on Lp-PLA2 levels in a cardiovascular disease free population derived from the PRINCE trial. After 12 weeks, Lp-PLA2 levels decreased by 22.1% among treated patients (vs. 7.8% among placebo group). Only 6% of the lowering of Lp-PLA2 by pravastatin could be accounted for by the lowering of LDL-C (Albert (2005) Atherosclerosis. 182:193-198).
Schaefer et al reported on the effects of atorvastatin versus other statins on fasting and postprandial c-reactive protein and Lp-PLA2 in patients with coronary heart disease versus control subjects. In this study the impact of various statins at the 40 mg/day dosage on Lp-PLA2 was compared. The study found that “atorvastatin is more effective than fluvastatin, lovastatin, pravastatin, or simvastatin for decreasing not only low density lipoprotein cholesterol but also hs-CRP and Lp-PLA2” (Schaefer (2005) Am J Cardiol. 95:1025-1032).
Saougos et al have reported on the effect of hypolipidemic drugs on Lp-PLA2. This is the first study to demonstrate that ezetimibe and rosuvastatin both lower Lp-PLA2 mass. Statin intolerant Type IIa dyslipidemics had an 18% reduction in Lp-PLA2 mass with ezetimibe 10 mg/day, and Type IIa dyslipidemics had a 29% reduction in Lp-PLA2 mass with rosuvastatin 10 mg/day. It also showed that fenofibrate 200 mg/day lowered Lp-PLA2 mass 32%, a finding similar to fenofibrate's effect on Lp-PLA2 mass in Type 2 DM (Saogos (2007) Arterioscler Thromb Vasc Biol. 27:2236-2243).
Muhlestein et al reported on The Reduction of Lp-PLA2 by statin, fibrate, and combination therapy among diabetic patients with mixed dyslipidemia. This study evaluated the effect of simvastatin 20 mg and fenofibrate 160 mg on Lp-PLA2 and CRP in type 2 diabetic patients with mixed dyslipidemia. Fenofibrate, simvastatin and the combination each lowered Lp-PLA2, and the effect was greatest among patients with baseline levels greater than the median. In this study, lipid-modifying agents lowered Lp-PLA2 by more than 25% (fenofibrate: 27%; simvastatin: 35%) (Muhlestein (2006) J Am Coll Cardiol. 48:396-401).
Rosenson et al recently reported on the effects of fenofibrate on Lp-PLA2 levels in non-diabetic patients with metabolic syndrome. In this study reduction in small LDL-P particles was significantly associated with the reduction in Lp-PLA2, suggesting that fenofibrate may lower Lp-PLA2 via plaque stabilization mediated by lowering small LDL-P (Rosenson (2008) Am Heart J. 155(3):499.e9-16).
Schmidt et al reported on the effects of eicosapentaenoic acid (EPA) on Lp-PLA2 levels in patients admitted to elective coronary angiography because of suspected coronary artery disease (CAD). The content of the marine n-3 fatty acid, eicosapentaenoic acid (EPA) in adipose tissue, a measure of long-term intake of seafood independently and inversely correlated with plasma levels of Lp-PLA2(r=−0.18, p<0.01). The results support that Lp-PLA2 may relate to CAD and that intake of marine n-3 fatty acids might reduce plasma Lp-PLA2 suggesting another mechanism by which n-3 fatty acids could reduce the risk of cardiovascular disease.
Kuvin et al reported on effects of extended-release niacin on lipoprotein particle size, distribution, and inflammatory markers in patients with coronary artery disease. This study evaluated the effect on Lp-PLA2 of adding niacin to stable coronary heart disease patients with well-managed baseline LDL levels of 76 mg/dL. While there was no significant change in baseline LDL levels after three months, niacin significantly lowered Lp-PLA2 by 20% (Kuvin (2006) Am J Cardiol. 98:743-745).
It appears from this study that Lp-PLA2 lowering was independent of LDL (which did not change) and that there appears to be residual opportunity to lower Lp-PLA2 in patients with low achieved LDL cholesterol, consistent with the concept that low achieved LDL alone may not assure that plaque has stabilized.
These studies identify therapies which benefit patients who have an increased risk of Lp-PLA2 related disease, e.g. CVD including coronary heart disease and stroke.
Care in the Acute Setting
The American Heart Association and American Stroke Association strongly urge people to seek medical attention as soon as possible if they believe they're having a stroke or heart attack. The sooner thrombolytic agents or other appropriate treatment is begun, the better the chances for recovery. One such thrombolytic agent is tissue plasminogen activator (tPA), a clot-busting drug. tPA is approved for use in certain patients having a heart attack or stroke. The drug can dissolve blood clots, which cause most heart attacks and strokes. tPA is the only drug approved by the U.S. Food and Drug Administration for the acute (urgent) treatment of ischemic stroke.
According to the American Heart Association studies have shown that thrombolytic agents, such as tPA, can reduce the amount of damage to the heart muscle and save lives. However, to be effective, they must be given within a few hours after symptoms begin. Administering tPA or other clot-dissolving agents is complex and is done through an intravenous (IV) line in the arm by hospital personnel. tPA has also been shown to be effective in treating ischemic stroke. This kind of stroke is caused by blood clots that block blood flow to the brain.
In 1996 the U.S. Food and Drug Administration (FDA) approved the use of tPA to treat ischemic stroke in the first three hours after the start of symptoms. This makes it very important for people who think they're having a stroke to seek help immediately. If given promptly, tPA can significantly reduce the effects of stroke and reduce permanent disability. tPA can only be given to a person within the first few hours after the start of stroke symptoms. The National Institute of Neurological Disorders and Stroke (NINDS) study suggested that 8 out of 18 stroke patients who receive tPA according to a strict protocol will recover by three months after the event without significant disability. This is compared to 6 out of 18 stroke patients (one-third) who recover substantially regardless of treatment. (N Engl J Med 333:1581-1587, 1995.)
While tPA or other thrombolytics can reduce disability from a heart attack or stroke, there is also a higher risk of bleeding. Studies vary in predicting the likelihood of complications, which include bleeding into the brain, other types of serious bleeding (e.g., gastrointestinal), and death. The NINDS study suggested that bleeding into the brain occurred in about 1 out of 18 patients receiving tPA (specifically, 5.8%). When this occurred, there was a 45 percent fatality rate. Several studies suggested treatment with “clot-dissolving” medications increases the number of patients who die following a stroke (JAMA 274(13):1017, 1995; Lancet 346:1509-1514, 1995; JAMA 276(12):961-6, 1996; NEJM 335(3):145, 1996; Lancet 352:1245-1251, 1998; JAMA 282(21):2019-26. 1999). Subsequent studies demonstrated that using tPA more liberally than is recommended in the NINDS protocol resulted in a higher rate of intracranial hemorrhage (JAMA 283:1151-1158, 2000; Cerebrovasc Dis 8 (suppl 4):48, 1998; Arch Intern Med 162:1994-2001, 2002; Cochrane Database Syst Rev. 2000:CD000213; Cochrane Database Syst Rev. 2000:CD000029). Complications are more likely when tPA is used in patients over 70 years old, those with more severe stroke, or those with glucose over 300 mg/dl.
Due to the severe risks associated with thrombolytics, it is important for physicians to weigh the possibility of benefit (e.g. improved function at 3 months) against the possibility of harm (severe bleeding or death). Stroke symptoms alone are insufficient to definitely diagnose stroke and, in patients with a stroke mimic, tPA use results only in potential adverse effects without any possibility of benefit. It is clear there is a need to identify patients who are suspected of having a cardiovascular event who will benefit from administration of thrombolytics (e.g. tPA).
Lp-PLA2 can be used to identify patients who will benefit from administration of thrombolytics. Lp-PLA2 expression has been shown to be higher in carotid plaques of patients with than without cardiac events (Herrmann (2009) Eur Heart J. 30(23):2930-8). In the event of a plaque rupture and vascular thrombus, high levels of Lp-PLA2 may be released into circulation from the rupture site. Measuring Lp-PLA2 levels of individuals suspected of having a stroke or myocardial infarction (e.g. individuals who present symptoms of a stroke or MI) can identify individuals who will benefit from standard thrombolytic therapy or and those who may need aggressive therapy including aggressive thrombolytic drug dosing, drug combinations and/or interventional and surgical therapies.
All publications and other materials described herein are used to illuminate the invention or provide additional details respecting the practice and are hereby incorporated by reference in their entirety.